一种基于空气扫描的锥束CT环形伪影校正方法

在分析锥束CT平板探测器校正方法及环形伪影残留原因的基础上,提出一种简便的基于空气扫描的锥束CT环形伪影校正方法。该方法首先在同一锥束CT系统中采用相同参数进行空气扫描和被测物体扫描,然后分别重建出系列切片图像,最后由被测物体切片图像与空气切片图像对应相减实现残留环形伪影的校正,同时起到一定的降噪作用。实验结果验证了该方法的可行性和有效性。

TQA工具在螺旋断层加速器质量控制中的初步研究

目的:运用螺旋断层加速器质控(TQA)工具对螺旋断层加速器(HT)空气扫描(Airscan)程序的连续监测,探索TQA工具在HT日检中的初步应用。方法:利用TQA工具Airscan模块记录HT每日的空气扫描程序运行数据,并针对连续6个月的Airscan数据进行趋势分析,评价每日铅门在随机架旋转过程中的稳定性,并对铅门旋转、监测电离室计数、探测器计数等长期变化趋势,以及对探测器输出稳定性予以监测。结果:根据TQA工具所测得6个月数据分析可得,HT铅门在随机架旋转过程中的位置偏差点到点能量通量差异(peak-to-peak fluence variation)平均为(0.11±0.00)mm;在Airscan运行前探测器测得的本底信号计数为(3859.61±3.37)counts,监测电离室测得本底信号计数为(505.85±9.17)counts;探测器测得的平均信号计数为(13553.96±195.14)counts,监测电离室测得的平均信号计数为(8422.14±10.88)counts,未发现异常信号点;探测器信号计数与监测电离室信号计数的比值在1.56~1.66之间浮动,平均值为1.61±0.02,表明探测器输出无异常,维持在一个相对稳定的状态。结论:TQA工具通过Airscan程序辅助监测HT的铅门随机架旋转的偏移以及探测器的输出稳定性,可对Airscan数据进行定量分析,能够对查找机器报错原因提供一定的指导意义。

Compact Scanning Tunneling Microscope with Large Scale Searching Capability for Mmultidisciplinary Applications

We present the design and performance of a home-built scanning tunneling microscope （STM）, which is compact （66 mm tall and 25 mm in diameter）, yet equipped with a 3D atomic precision piezoelectric motor in which the Z coarse approach relies on a high simplic-ity friction-type walker （of our own invention） driven by an axially cut piezoelectric tube. The walker is vertically inserted in a piezoelectric scanner tube （PST） with its brim laying at on the PST end as the inertial slider （driven by the PST） for the XZ （sample plane） motion. The STM is designed to be capable of searching rare microscopic targets （defects, dopants, boundaries, nano-devices, etc.） in a macroscopic sample area （square millimeters） under extreme conditions （low temperatures, strong magnetic elds, etc.） in which it ts. It gives good atomic resolution images after scanning a highly oriented pyrolytic graphite sample in air at room temperature.

Preparation of basic magnesium carbonate and its thermal decomposition kinetics in air

The thermal decomposition process of basic magnesium carbonate was investigated. Firstly, Basic magnesium carbonate was prepared from magnesite, and the characteristics of the product were detected by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. Subsequently, the thermal decomposition process of basic magnesium carbonate in air was studied by thermogravimetry-differential thermogravimetry （TG-DTG）. The results of XRD confirm that the chemical composition of basic magnesium carbonate is 4MgCO3·Mg（OH）2·4H2O. And the SEM images show that the sample is in sheet structure, with a diameter of 0.1-1 μm. The TG-DTG results demonstrate that there are two steps in the thermal decomposition process of basic magnesium carbonate. The apparent activation energies （E） were calculated by Flyrm-Wall-Ozawa method. It is obtained from Coats-Redfem＇s equation and Malek method that the mechanism functions of the two decomposition stages are D3 and A1.5, respectively. And then, the kinetic equations of the two steps were deduced as well.

Spatio-temporal Variation of Arctic Sea Ice in Summer from 2003 to 2013

The variation in Arctic sea ice has significant implications for climate change due to its huge influence on the global heat balance. In this study, we quantified the spatio-temporal variation of Arctic sea ice distribution using Advanced Microwave Scanning Radiometer(AMSR-E) sea-ice concentration data from 2003 to 2013. The results found that, over this period, the extent of sea ice reached a maximum in 2004, whereas in 2007 and 2012, the extent of summer sea ice was at a minimum. It declined continuously from 2010 to 2012, falling to its lowest level since 2003. Sea-ice extent fell continuously each summer between July and mid-September before increasing again. It decreased most rapidly in September, and the summer reduction rate was 1.35 × 10~5 km^2/yr, twice as fast as the rate between 1979 and 2006, and slightly slower than from 2002 to 2011. Area with >90% sea-ice concentration decreased by 1.32 × 10~7 km^2/yr, while locations with >50% sea-ice concentration, which were mainly covered by perennial ice, were near the North Pole, the Beaufort Sea, and the Queen Elizabeth Islands. Perennial Arctic ice decreased at a rate of 1.54 × 10~5 km^2 annually over the past 11 years.

Pseudopneumoperitoneum in chronic intestinal pseudo-obstruction:A case report

Chronic intestinal pseudo-obstruction(CIPO) is a rare disease due to a severe gastrointestinal motility disorder which may mimic,on both clinical and radiological grounds,mechanical obstruction.We report a case of a 26-year-old woman who presented to our institution for plain abdominal radiography for referred long-lasting constipation with recurrent episodes of abdominal pain and distension.At X-ray,performed both in the upright and supine position,an isolated air-fluid level was depicted in the left flank,together with a number of radiological signs suggestive of pneumoperitoneum.First,subphrenic radiolucency could be observed in the upright film.Second,the intestinal wall of some jejunal loops appeared to be outlined in the right flank.Third,the inferior cardiac border was clearly depicted in the upright film.The patient however had no evidence ofperitoneal signs but only hypoactive bowel movements.Unenhanced multi-detector computed tomography(MDCT) of the abdomen and pelvis was therefore performed.MDCT revealed abnormal air-driven distension of the small and large bowel,without evidence of extraluminal air.All radiological signs of pneumoperitoneum turned out to be false-positive results.The patient was submitted to pan-colonoscopy and to anorectal manometry to rule out Hirshprung's disease,and was finally discharged with a diagnosis of CIPO.

Analysis of Systematic Error Influences on Accuracy of Airborne Laser Scanning Altimetry

The error sources related to the laser rangefinder, GPS and INS are analyzed in details. Several coordinates systems used in airborne laser scanning are set up, and then the basic formula of system is given. This paper emphasizes on discussing the kinematic offset correction between GPS antenna phase center and laser fired point. And kinematic time delay influence on laser footprint position, the ranging errors, positioning errors, attitude errors and integration errors of the system are also explored. Finally, the result shows that the kinematic time delay can be neglected as compared with other error sources. The accuracy of the coordinates is not only influenced by the amplitude of the error, but also controlled by the operation parameters such as flight height, scanning angle amplitude and attitude magnitude of the platform.

The Effect of Air Pollution on Chenopodium album L. Pollen Structure

Air pollution is harm and discomfort to human or other living organisms, it also causes damage to the environment. The aim of this project was to study the effect of air pollutions on structure and pollen grains development in Chenopodium album. Anthers of Chenopodium album L. were collected at different stages of development from control （less polluted） and polluted areas （mainly SO2, NO2, CO and APM）. Structure and development of pollen grains were studied and compared. The effects of pollution on pollen structure was investigated under Light and Scanning electron microscopy and the results showed that when pollen grains were exposed to polluted air they became abnormality in form and covered with large amounts of pollutants compared to control ones. Pollen abnormalities were seen as irregularity, shrinkage, thinning and breakage of the exine. Cellular material release was induced also. The data presented suggest that prolonged exposures of plants to air pollution may cause different biological effects at the cellular tissue and organ levels.

Arc corrosion behavior of Cu-Ti_3AlC_2 composites in air atmosphere

The arc corrosion evolution of Cu-20 vol.% Ti_3 AlC_2 cathodes is presented here. After eroded by 3, 4, 5, 6, 7, 8, 9, 10 kV DC voltage, respectively, the surface morphologies were characterized by field emission scanning electron microscope with craters and protrusions. Compared to small craters and dense protrusions of the morphology by high voltage, the eroded surface was covered with bigger craters and sparse protrusions at low voltage. No crack was discovered on the surface even at 10 kV. By means of energy dispersive spectroscopy and Raman spectroscopy, the decomposition of Cu-20 vol.% Ti_3 AlC_2 cathode to CuO,Al__2 O_3 and TiO_2 were proved. Meanwhile, W anode is oxidized to WO_2. The peak current increases with the increasing breakdown voltage, which is recorded by a digital memory oscilloscope.

A novel composite(FMC)to serve as a durable 3D-clam-shaped bifunctional cathode catalyst for both primary and rechargeable zinc-air batteries

Novel and highly durable air cathode electrocatalyst with three dimensional （3D）-clam-shaped structure, MnO2 nanotubes-supported Fe2O3 （Fe2O3/MnO2） composited by carbon nanotubes （CNTs） （（Fe2O3/ MnO2）3/4-（CNTs）1/4） is synthesized using a facile hydrothermal process and a following direct heat- treatment in the air. The morphology and composition of this catalyst are analyzed using scanning elec- tronic microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD） and energy dispersive X-ray spectroscopy （EDX）. The morphology characteristics reveal that flower-like Fe2O3 parti- cles are highly dispersed on both MnO2 nanotubes and CNT surfaces, coupling all three components firmly. Electrochemical measurements indicate that the synergy of catalyst exhibit superior bi- functional catalytic activity for both oxygen reduction reaction （ORR） and oxygen evolution reaction （OER） as well as stability than Pt/C and lrO2 catalysts. Using these catalysts for air-cathodes, both primary and rechargeable zinc-air batteries （ZABs） are assembled for performance validation. In a primary ZAB, this 3D-clamed catalyst shows a decent open circuit voltage （OCV, -1.48 V） and a high discharge peak power density （349 mW cm 2）, corresponding to a coulomhic efficiency of 92%. In a rechargeahle ZABs with this bifunctional catalyst, high OCV （〉1.3 V） and small charge-discharge voltage gap （〈1.1 V） are achieved along with high specific capacity （780 mAh g 1 at 30 mA cm-2） and robust cycle-life （1,390 cycles at cycle profile of 20 mA/10 min）.

Stability analysis of quasicrystal torsion micromirror actuator based.on the strain gradient theory

Electrostatic torsional micromirrors are widely applied in the fields·of micro-optical switches,optical attenuators,optical scanners,and optical displays.In previous lectures,most of the micromirrors were twisted along the urtiaxial or biaxial direction,which limited the range of light reflection.In this·paper,a quasicrystal torsional micromirror that can be deflected in any direction is designed and the dynamic model of the electrostatically driven micromirror is established.The static and dynamic phenomena and pull-in characteristics are analyzed through the numerical solution of the strain gradient theory.The results of three kinds of mirror deflection directions are compared and analyzed.The results show the significant differences in the torsion models with different deflection axis directions.When the deflection angle along the oblique axis reaches 45°,the instability voltage is the smallest.The pull-in instability voltage increases with the increment ofphonon-phason coupling elastic modulus and phason elastic modulus.The perrriittivity of quasicrystal,the strain gradient parameter,and the air damping influence the torsion of the micromirror dynaniic system.A larger pull-in instability voltage generates with the decrease of surface distributed forces.